want to randomly drop packets based on percent

want to randomly drop packets based on percent

[George Nychis]

Hey,

I'm using the 2.4.32 kernel with madwifi and iproute2 version 
2-2.6.16-060323.tar.gz

I wanted to insert artificial packet loss based on a percent so i found:
network emulab qdisc could do it, so i compiled support into the kernel 
and tried:
tc qdisc change dev eth0 root netem loss .1%

however i keep getting the error
RTNETLINK answer: Invalid argument

I am not sure how to go about solving this problem for now, so if anyone 
has any suggestions i'd greatly appreciate it.

I really only need to drop random packets being forwarded through 
ip_forward ... however randomly dropping any packet based on a % is 
sufficient so I figured netem would be great.

So in the meantime I figured I would try to insert packet loss in 
ip_forward.c by generating a random number and dropping based on that. 
I could goto drop; depending on the number in the function int 
ip_forward(struct sk_buff *skb)

But then I ran into the problem of properly seeding the random number 
generator... srand(time(0)) is one way... however time() returns 
seconds, therefore i would drop multiple packets in a single second if I 
used this method which is very undesirable.  What is the proper way to 
generate a random number here?

Thanks!
George

Re: want to randomly drop packets based on percent

[Jan Engelhardt]

>
> I'm using the 2.4.32 kernel with madwifi and iproute2 version
> 2-2.6.16-060323.tar.gz
>
> I wanted to insert artificial packet loss based on a percent so i found:
> network emulab qdisc could do it, so i compiled support into the kernel and
> tried:
> tc qdisc change dev eth0 root netem loss .1%

You could just use the 'random' match module from netfilter/POMng, but I 
doubt it will compile out-of-the-box on 2.4.32. It would then be as simple 
as
	iptables -t mangle -I PREROUTING -m random --average 1 -j DROP

> I really only need to drop random packets being forwarded through ip_forward
> ... however randomly dropping any packet based on a % is sufficient so I
> figured netem would be great.

Jan Engelhardt
-- 

Re: want to randomly drop packets based on percent

[Stephen Hemminger]

On Mon, 17 Apr 2006 03:38:33 -0400
George Nychis <gnychis@cmu.edu> wrote:

> Hey,
> 
> I'm using the 2.4.32 kernel with madwifi and iproute2 version 
> 2-2.6.16-060323.tar.gz
> 
> I wanted to insert artificial packet loss based on a percent so i found:
> network emulab qdisc could do it, so i compiled support into the kernel 
> and tried:
> tc qdisc change dev eth0 root netem loss .1%

Most likely, you the version of the kernel you are running was not
configured with netem enabled.

Re: want to randomly drop packets based on percent

[George Nychis]

Stephen Hemminger wrote:

>On Mon, 17 Apr 2006 03:38:33 -0400
>George Nychis <gnychis@cmu.edu> wrote:
>
>  
>
>>Hey,
>>
>>I'm using the 2.4.32 kernel with madwifi and iproute2 version 
>>2-2.6.16-060323.tar.gz
>>
>>I wanted to insert artificial packet loss based on a percent so i found:
>>network emulab qdisc could do it, so i compiled support into the kernel 
>>and tried:
>>tc qdisc change dev eth0 root netem loss .1%
>>    
>>
>
>Most likely, you the version of the kernel you are running was not
>configured with netem enabled.
>
>  
>
Hey Stephen,

I have netem enabled in the kernel... I've checked this numerous times.  
I enabled it under Networking Options -> QoS -> Network emulator.  I 
even did a make clean, make mrproper, and rebuilt from scratch.

Maybe I'll try compiling it as a module and see if anything changes.

Any other ideas?

----

In response to Matt:
Thank you!

One last question, if I take this route, what is the easiest way to 
allow me to change the packet loss without hard coding a percent into 
the kernel?

Re: want to randomly drop packets based on percent

[Stephen Hemminger]

On Mon, 17 Apr 2006 18:30:51 -0400
George Nychis <gnychis@cmu.edu> wrote:

> 
> 
> Stephen Hemminger wrote:
> 
> >On Mon, 17 Apr 2006 03:38:33 -0400
> >George Nychis <gnychis@cmu.edu> wrote:
> >
> >  
> >
> >>Hey,
> >>
> >>I'm using the 2.4.32 kernel with madwifi and iproute2 version 
> >>2-2.6.16-060323.tar.gz
> >>
> >>I wanted to insert artificial packet loss based on a percent so i found:
> >>network emulab qdisc could do it, so i compiled support into the kernel 
> >>and tried:
> >>tc qdisc change dev eth0 root netem loss .1%
             ^^^^^^

You need to do add not change. Add will set the queue discipline
to netem (default is pfifo_fast).  Change is for changing netem parameters
after it is loaded.

Re: want to randomly drop packets based on percent

[George Nychis]

Stephen Hemminger wrote:

>On Mon, 17 Apr 2006 18:30:51 -0400
>George Nychis <gnychis@cmu.edu> wrote:
>
>  
>
>>Stephen Hemminger wrote:
>>
>>    
>>
>>>On Mon, 17 Apr 2006 03:38:33 -0400
>>>George Nychis <gnychis@cmu.edu> wrote:
>>>
>>> 
>>>
>>>      
>>>
>>>>Hey,
>>>>
>>>>I'm using the 2.4.32 kernel with madwifi and iproute2 version 
>>>>2-2.6.16-060323.tar.gz
>>>>
>>>>I wanted to insert artificial packet loss based on a percent so i found:
>>>>network emulab qdisc could do it, so i compiled support into the kernel 
>>>>and tried:
>>>>tc qdisc change dev eth0 root netem loss .1%
>>>>        
>>>>
>             ^^^^^^
>
>You need to do add not change. Add will set the queue discipline
>to netem (default is pfifo_fast).  Change is for changing netem parameters
>after it is loaded.
>
>  
>
bahhh I see... the wiki has "change" instead of add.  Now i'm running 
into another problem, I have an XCP qdisc that I have already added via:
tc qdisc add dev ath0 root xcp capacity 54Mbit size 500

therefore when I also try to incorperate loss:
tcq disc add dev ath0 root netem loss .1%

I get:
RTNETLINK answers: File exists

Is it possible to use two qdiscs on the same interface?

Thanks!
George

Re: want to randomly drop packets based on percent

[Stephen Hemminger]

O
> >>>>I wanted to insert artificial packet loss based on a percent so i found:
> >>>>network emulab qdisc could do it, so i compiled support into the kernel 
> >>>>and tried:
> >>>>tc qdisc change dev eth0 root netem loss .1%
> >>>>        
> >>>>
> >             ^^^^^^
> >
> >You need to do add not change. Add will set the queue discipline
> >to netem (default is pfifo_fast).  Change is for changing netem parameters
> >after it is loaded.
> >
> >  
> >
> bahhh I see... the wiki has "change" instead of add.  Now i'm running 
> into another problem, I have an XCP qdisc that I have already added via:
> tc qdisc add dev ath0 root xcp capacity 54Mbit size 500
> 

Wiki reads as a set of examples.  First uses, "add" after that "change".


> therefore when I also try to incorperate loss:
> tcq disc add dev ath0 root netem loss .1%
> 
> I get:
> RTNETLINK answers: File exists
> 
> Is it possible to use two qdiscs on the same interface?
> 

No, but netem is "classful" so you can put xcp inside netem.
Look at the token bucket example on the wiki.

Re: want to randomly drop packets based on percent

[George Nychis]

Stephen Hemminger wrote:

>O
>  
>
>>>>>>I wanted to insert artificial packet loss based on a percent so i found:
>>>>>>network emulab qdisc could do it, so i compiled support into the kernel 
>>>>>>and tried:
>>>>>>tc qdisc change dev eth0 root netem loss .1%
>>>>>>       
>>>>>>
>>>>>>            
>>>>>>
>>>            ^^^^^^
>>>
>>>You need to do add not change. Add will set the queue discipline
>>>to netem (default is pfifo_fast).  Change is for changing netem parameters
>>>after it is loaded.
>>>
>>> 
>>>
>>>      
>>>
>>bahhh I see... the wiki has "change" instead of add.  Now i'm running 
>>into another problem, I have an XCP qdisc that I have already added via:
>>tc qdisc add dev ath0 root xcp capacity 54Mbit size 500
>>
>>    
>>
>
>Wiki reads as a set of examples.  First uses, "add" after that "change".
>
>
>  
>
>>therefore when I also try to incorperate loss:
>>tcq disc add dev ath0 root netem loss .1%
>>
>>I get:
>>RTNETLINK answers: File exists
>>
>>Is it possible to use two qdiscs on the same interface?
>>
>>    
>>
>
>No, but netem is "classful" so you can put xcp inside netem.
>Look at the token bucket example on the wiki.
>
>  
>
Okay I'm slightly confused... I would like to have the traffic  traverse 
both the XCP qdisc and the netem qdisc... looking through the wiki it 
shows me how to classify two sets of traffic, but how do i push all 
traffic through both?

Re: want to randomly drop packets based on percent

[George Nychis]

Stephen Hemminger wrote:

>O
>  
>
>>>>>>I wanted to insert artificial packet loss based on a percent so i found:
>>>>>>network emulab qdisc could do it, so i compiled support into the kernel 
>>>>>>and tried:
>>>>>>tc qdisc change dev eth0 root netem loss .1%
>>>>>>       
>>>>>>
>>>>>>            
>>>>>>
>>>            ^^^^^^
>>>
>>>You need to do add not change. Add will set the queue discipline
>>>to netem (default is pfifo_fast).  Change is for changing netem parameters
>>>after it is loaded.
>>>
>>> 
>>>
>>>      
>>>
>>bahhh I see... the wiki has "change" instead of add.  Now i'm running 
>>into another problem, I have an XCP qdisc that I have already added via:
>>tc qdisc add dev ath0 root xcp capacity 54Mbit size 500
>>
>>    
>>
>
>Wiki reads as a set of examples.  First uses, "add" after that "change".
>
>
>  
>
>>therefore when I also try to incorperate loss:
>>tcq disc add dev ath0 root netem loss .1%
>>
>>I get:
>>RTNETLINK answers: File exists
>>
>>Is it possible to use two qdiscs on the same interface?
>>
>>    
>>
>
>No, but netem is "classful" so you can put xcp inside netem.
>Look at the token bucket example on the wiki.
>
>  
>
Sorry, I was looking at the LARTC guide, completely skipped over the 
blatently obvious block of commands you were pointing me too :P

Thanks!
George

Re: want to randomly drop packets based on percent

[Bodo Eggert]

George Nychis <gnychis@cmu.edu> wrote:

> But then I ran into the problem of properly seeding the random number
> generator... srand(time(0)) is one way... however time() returns
> seconds, therefore i would drop multiple packets in a single second if I
> used this method which is very undesirable.  What is the proper way to
> generate a random number here?

You seed the random generator once, not each time you use it.

-- 
Ich danke GMX dafür, die Verwendung meiner Adressen mittels per SPF
verbreiteten Lügen zu sabotieren.